The present invention relates generally to electrical utility meters, and in particular, electrical utility meters for use in polyphase power configurations.
Electrical utility service providers, or simply utilities, monitor energy usage by customers through electrical utility meters. Electrical utility meters track the amount of energy consumed, typically measured in kilowatt-hours (xe2x80x9ckwhxe2x80x9d), at each customer""s facility. The utility uses the consumption information primarily for billing, but also for resource allocation planning and other purposes.
Most utilities generate polyphase electrical power, and typically three phase power. Polyphase electrical power is alternating current electrical power that is supplied on a plurality of power supply lines wherein the voltage waveform on each of the power supply lines has a unique phase angle. While only a single phase of the polyphase electrical power is typically provided for single family dwellings, true polyphase electrical power is typically provided to larger facilities such as commercial and industrial facilities.
Polyphase electrical power is provided to customers in a plurality of configurations, known as service types. A service type is typically defined by the nominal voltage level and a wiring configuration. A wiring configuration is further defined by the number of wires (three wire or four wire) and the wiring relationship between the phases (wye or delta). For example, a 120 volt four wire service type has a nominal voltage level of 120 volts and a four wire wye wiring configuration. The most commonly-used service types are standardized and are well-known to those of ordinary skill in the art.
Different standard watt-hour meter types, known as meterforms, are used to measure the power consumption for the various service types. Meter forms are distinguished by, among other things, the method by which they determine the amount of consumed power. The consumed power determination method used by a particular meter form is generally appropriate for some service types but not for others. The meter form that is appropriate for use in a particular customer facility also depends on a number of other factors, including: the maximum level of current expected; the accuracy needed; cost; and whether the wiring configuration has a common neutral. The commonly-used meter forms include those designated as 5S, 45S, 6S, 36S, 9S, 16S, 12S and 25S meter forms.
The trend of the metering industry has been to reduce the number of meter forms required to meter the common service types. A reduction in the number of meter forms provides the advantage of reducing the different types of meter hardware that must be manufactured and inventoried. Accordingly, many of the meter forms currently used are applicable to a plurality of service types. In many instances, a single meter form may be used for a plurality of nominal voltage levels if the wiring configuration (wye or delta, three or four wire) is kept constant. This is possible because the same power calculations generally apply to all service types having the same wiring configuration regardless of the nominal voltage. For example, a 9S meter performs the same power calculations for 120, 240 and 480 volt four wire delta configurations, and is therefore compatible with all three of those service types. Likewise, it is well-known that 6S and 36S meter forms may be used for both 120 and 277 volt four wire wye service types, and further only require measurements from two of the three phases.
In addition to the reduction of meter forms, another development in electrical utility meters are electronic meters. Electronic meters replace the older inductive spinning disc meter design. Electronic meters have the advantage of providing additional features beyond straight-forward power consumption metering. Electronic meters, may, for example, track energy demand, power factor, and per phase power measurements. Electronic meters are also capable of fairly sophisticated diagnostics. For example, U.S. Pat. No. 5,469,049 to Briese et al. teaches a diagnostic toolbox that is built into the meter. The diagnostic toolbox in the Briese et al. device measures per phase voltage and current magnitude and phase angles, and then compares the measured values with expected values to determine whether an error is present. In addition, electronic meters may alter their power calculations to accommodate further service types, thereby increasing the versatility of the meter forms.
The prior art electronic meters thus offer greater features and functionality than was previously available in inductive spinning disc meters. One drawback to the prior art electronic meters, however, is that some of the more advanced features require that the meter be preconfigured for the particular service type to which it is connected. For example, in the Briese et al., the service type must be programmed into the software before the meter can perform the diagnostic toolbox operations. Otherwise, the diagnostic toolbox would not be able to determine what voltage magnitude and phase angle readings are to be expected.
To provide such information, the identification of the service type may be provided as input to the meter during its manufacture (preconfiguring) or provided as input during installation by a technician. Neither solution is optimal. Preconfiguring the meter during its manufacture introduces complexity into the inventory and delivery systems, thereby reducing the efficiency that the consolidation of meter forms was intended to create. Likewise, requiring that a technician provide such input to the meter during installation undesirably increases the complexity associated with installing the meters.
The present invention overcomes these as well as other shortcomings of the prior art by automatically identifying the service type. A method according to the present invention, which is performed in an electric utility meter connected to a polyphase electrical system, comprises first obtaining measured voltage magnitude and phase angle data for a plurality of phases in a polyphase electrical system and then identifying the present electrical service type based on the measured voltage magnitude and phase angle data.
An exemplary embodiment of the present invention includes an arrangement for use in an electrical utility meter, the electrical utility meter operable to be connected to a plurality of electrical service types. The arrangement is operable to identify a present service type, the present service type being one of the plurality of electrical service types to which the electrical utility meter is connected. The arrangement comprises: a conversion circuit for obtaining measured voltage magnitude and phase angle data for a plurality of phases in a polyphase electrical system; a memory; and a processor connected to said memory and said conversion circuit. The processor is operable to execute programming steps stored in the memory to receive the measured voltage magnitude and phase angle data from the conversion circuit and identify the present electrical service type based on the measured voltage magnitude and phase angle data.
Once the service type is identified, it may then be provided on a visible display on the meter, used to configure the conversion circuit for accurate metering, or used in subsequent diagnostic routines, as well as any combination of the above.